At the end of the introduction, Nevin compares this progressive sanctification of the Church to the life of individuals and says that they are not only analogous, but they are completely codependent. In other words, the ultimate sanctification and salvation of individuals is in the salvation of the Church as a whole.
“Only indeed as it is comprehended in this general process, can the particular process by which the salvation of the single Christian is accomplished, from the new birth to the morning of the resurrection, be carried successfully forward. He is saved in the Church, the mystical body of Christ; and can become complete, only as the whole is made complete which he is a part. His resurrection accordingly, the last result of the organic power of his nature, will be reached only in connection with the consummation of the life of the Church as a whole, when in the fullest and most glorious sense, old things shall have passed away and all things become new.” (The Principle of Protestantism, 25-26)